The present invention relates to an apparatus for adjusting a basic position of a camshaft adjustment unit for infinitely varying rotational relations between a camshaft and a crankshaft of an internal combustion engine.
Typically, the camshaft adjusting mechanism is attached at one end surface of the camshaft (or a shaft to be adjusted) and includes a crankshaft-fixed structure such as timing pulley which is driven by the crankshaft via a timing belt or chain, a camshaft-fixed structure such as a drive wheel, and an adjusting piston which reciprocates between two end positions for rotating the crankshaft-fixed structure and the camshaft-fixed structure relative to one another. Such adjustment units are known in various designs. The installation of the adjustment unit to the camshaft of an internal combustion engine or to an intermediate shaft positioned between the crankshaft and two camshafts is normally attained by fixedly mounting the camshafts in place and randomly installing the adjustment unit in a centering receptacle of the camshaft. Then, the adjustment unit is screwed with a central screw fastener to the camshaft to such an extent that a rotation of the adjustment unit relative to the camshaft (or intermediate shaft) is still possible. The timing belt or chain is then laid around the drive wheel of the camshaft and tightened. As a result of the still possible relative rotation between the adjustment unit and the camshaft, the adjustment unit can then be positioned to occupy its basic disposition, i.e. can be so turned that the adjusting piston occupies an end position, called retard position. Subsequently, the central screw fastener is further tightened to fixedly secure the adjustment unit onto the camshaft, and the timing belt or chain is tensioned to exhibit the necessary operational tension.
Practice has shown, however, that during tightening of the adjustment unit upon the camshaft and/or during tensioning of the timing belt, the adjusting piston shifts from its basic position after assembly as a result of the torque being transmitted during installation.
Although an incorporated associated electronic engine control for the adjustment unit is capable to recognize the angular relation between the crankshaft and the camshaft, the basic position of the adjusting piston is still set as fixed parameter. Thus, a shift of the adjusting piston from the basic position has the consequence that after assembly, the existing actual state does no longer correspond to the parameters of the control such as stroke, phase position, opening angle of the valves. This may lead to undesired shifts of the valve timing and in a worst case scenario to a collision of the valve with the piston.